Frp molded article and method of producing the same

ABSTRACT

An FRP molded article molded by hot runner injection molding with a mixture of thermoplastic resin and reinforcing fibers of 0.1-7 mm in average length dispersed in the thermoplastic resin; and a hot runner injection molding method therefore. The molded article is preferable for use as a housing for electronic terminal equipment, cellular phones, etc.

TECHNICAL FIELD

[0001] The present invention relates to an FRP molded article and aproduction process thereof.

[0002] The FRP molded article of the invention comprises a thermoplasticresin used as a matrix resin and reinforcing fibers having an averagefiber length of 0.1 to 7 mm dispersed in the matrix resin. The FRPmolded article is thin-walled and has excellent mechanical propertiesand low volume resistivity. It can be preferably used as a housing of anelectronic terminal machine or device, portable cellular phone, etc.

[0003] The molded article of the invention can be produced by ahot-runner injection molding method.

BACKGROUND ART

[0004] Injection-molded articles made from synthetic resins are widelyused, for example, as structural parts such as functional parts andmechanical parts, and housings of office machines and devices,electronic terminal machines and devices, portable cellular phones, etc.Especially the injection-molded articles made from carbonfiber-reinforced resins are widely used as housings of computer terminalmachines and apparatuses, portable cellular phones, etc., since theyhave excellent mechanical properties and high electromagnetic waveshielding capability.

[0005] Molded thermoplastic resin articles are mostly produced byinjection molding methods. When a desired injection molded article madefrom a thermoplastic resin is produced by an injection molding method,the portions called sprue runners to be thrown away after molding areformed in addition to the portion destined to be a product. Usually therate by weight of the sprue runners to the molded article is small, andthe shapes of the sprue runners do not pose any large problem.

[0006] However, in the case where a molded article reinforced by carbonfibers or other reinforcing fibers is produced by an injection moldingmethod, especially in the case where a complicatedly shaped large-sizedmolded article like a housing of a terminal machine or device of apersonal computer is produced by an injection molding method, a moltenresin composed of a mixture of a thermoplastic resin and reinforcingfibers is poor in flowability. Therefore, multi-gate molding, in whichmany gates are used for injecting the molten resin, is employed. In thiscase, the rate by weight of a sprue runner portion in a molded articlethereto becomes large and as a result material to be thrown awayincreases.

[0007] A thermoplastic resin reinforced by reinforcing fibers is high inthe unit cost of material compared with general engineering plastics.Therefore, in the conventional molding methods, in which the number ofsprue runners to be thrown away is large, the cost of the molded articleis inevitably higher.

[0008] If sprue runners exist, flow resistance acts on the molten resinflowing there, to break and thin the reinforcing fibers contained in themolten resin. As a result, the physical properties of the obtainedmolded article decline.

[0009] Injection molding using hot runners is already practically usedfor molding of thermoplastic engineering plastics not containingreinforcing fibers.

[0010] On the other hand, several cases are known, in which athermoplastic resin containing reinforcing fibers is molded by means ofinjection molding using hot runners. However, no attempt is known, inwhich a thermoplastic resin containing carbon fibers as reinforcingfibers is molded by means of injection molding using hot runners.

[0011] One reason is that in the case where a thermoplastic resinreinforced by reinforcing fibers is molded by means of hot-runnerinjection molding, it is feared that the product becomes poor inappearance and is warped. As another reason, since no means fortechnically overcoming the feared defects has been examined, moldedarticle manufacturers consider that there is a risk in employing thetechnique for producing sellable molded articles.

[0012] An object of the invention is to greatly reduce sprue runnersthat raise the cost of the injection-molded article made from a highlyfunctional material, i.e., a thermoplastic resin reinforced byreinforcing fibers, and another object is to provide an injection moldedarticle made from a thermoplastic resin reinforced by reinforcingfibers, which is substantially free from defects such as poor appearanceand warping.

DISCLOSURE OF THE INVENTION

[0013] The FRP molded article of the invention to achieve theabove-mentioned objects is as follows:

[0014] An FRP molded article comprising a thermoplastic resin andresin-reinforcing fibers having an average fiber length of 0.1 to 7 mmdispersed in said thermoplastic resin, produced by a hot-runnerinjection molding.

[0015] In the FRP molded article of the invention, it is preferable thatthe fibers are at least one kind of fibers selected from a groupconsisting of carbon fibers, glass fibers and aramid fibers.

[0016] In the FRP molded article of the invention, it is preferable thatthe length of the hot-runner sprue used in the hot-runner injectionmolding is 10 to 600 mm.

[0017] In the FRP molded article of the invention, it is preferable thatthe depression formed by the tip of a gate pin used for opening andclosing a gate provided at the tip of the hot-runner sprue exists on thesurface of the molded article.

[0018] In the FRP molded article of the invention, it is preferable thatthe depression has a diameter of 0.1 to 10 mm and a depth of 2 mm orless.

[0019] In the FRP molded article of the invention, it is preferable thatthe hot-runner injection molding has plural hot-runner sprues havingopening-closing gates at the tips thereof respectively and each of theopening-closing gates is controlled independently each other.

[0020] In the FRP molded article of the invention, it is preferable thatthe hot-runner sprue comprises plural hot-runner sprues and a resinpassing through a first sprue of an injection molding machinecommunicating to the plural hot-runner sprues passes through respectiveresin passages and is injected from the respective gates provided at thetips of the respective hot-runner sprues substantially at the sametiming.

[0021] In the FRP molded article of the invention, it is preferable thatthe geometrical lengths of the respective resin passages are equal toeach other.

[0022] In the FRP molded article of the invention, it is preferable thatthere are time differences in the opening and closing timings of therespective gates.

[0023] In the FRP molded article of the invention, it is preferable thatthe molded article is an equipment body.

[0024] The process for producing the FRP molded article of the inventionfor achieving the above-mentioned objects is as follows:

[0025] A process for producing an FRP molded article, comprising:

[0026] (a) a first step, in which resin pellets having resin-reinforcingfibers having an average fiber length of 0.1 to 7 mm mixed in athermoplastic resin used as a matrix resin are heated and molten at 220to 350° C. in a resin-melting cylinder of an injection molding machine,to prepare a molten resin having the fibers dispersed therein, and

[0027] (b) a second step, in which the molten resin obtained in thefirst step is fed to a hot-runner sprue through a first sprue of theinjection molding machine and further through the resin passage of ahot-runner injection molding apparatus; the gate of the hot-runner sprueis opened and closed to control the start and end of injection of themolten resin into a cavity of a mold used for molding an article; themolten resin fed into the cavity is solidified in the mold; the mold isopened; and the molded article is taken out.

[0028] In the process for producing an FRP molded article of theinvention, it is preferred that the length of the hot-runner sprue is 10to 600 mm.

[0029] In the process for producing an FRP molded article of theinvention, it is preferred that the gate is opened and closed by a gatepin going into and out of the gate, and that a depression is formed onthe surface of the molded article by the tip of the gate pin.

[0030] In the process for producing an FRP molded article of theinvention, it is preferred that the depression has a diameter of 0.1 to10 mm and a depth of 2 mm or less.

[0031] In the process for producing an FRP molded article of theinvention, it is preferred that the hot-runner sprue comprises pluralhot-runner sprues and the opening and closing of the respective gatesprovided at the tips of the plural hot-runner sprues can be controlledrespectively independently.

[0032] In the process for producing an FRP molded article of theinvention, it is preferred that the hot-runner sprue comprises pluralhot-runner sprues, and the resin passing through a first sprue of aninjection molding machine communicating to the plural hot-runner spruespasses through respective resin passages and is injected from therespective gates at the tips of the respective hot-runner sprues at thesame timing.

[0033] In the process for producing an FRP molded article of theinvention, it is preferred that the geometrical lengths of therespective resin passages are equal to each other.

[0034] In the process for producing an FRP molded article of theinvention, it is preferred that there are time differences in theopening and closing timings of the respective gates.

BRIEF DESCRIPTION OF THE DRAWINGS

[0035]FIG. 1 is a typical side view of an injection molding apparatusprovided with a hot runner for producing a molded article of theinvention.

[0036]FIG. 2 is a typical vertical sectional view of a mold section ofthe apparatus shown in FIG. 1.

[0037]FIG. 3 is a typical side view of a hot-runner sprue installed inthe mold section shown in FIG. 2.

[0038]FIG. 4 is a typical vertical sectional view of the hot-runnersprue shown in FIG. 3.

[0039]FIGS. 5A and 5B are typical vertical sectional views forexplaining opening and closing of a valve gate of a hot-runner sprue.

[0040]FIG. 6A is a typical vertical sectional view of a mold section ofa conventional injection molding apparatus having no hot-runner sprue.

[0041]FIG. 6B is a typical vertical sectional view of another example ofa mold section of an injection molding apparatus having a hot runnerused for producing a molded article of the invention.

[0042]FIG. 7 is a typical vertical sectional detail view of the hotrunner in the mold section shown in FIG. 6B.

[0043]FIG. 8 is a typical vertical sectional detail view of anotherexample of a hot runner different from the hot runner shown in FIG. 7.

[0044]FIG. 9 is a typical vertical sectional detail view of anotherexample of a hot runner different from the hot runner shown in FIG. 7.

[0045]FIG. 10 is a typical perspective view of an example of a gatelayout of hot-runner sprues in a mold section of an injection moldingapparatus having hot runners used for producing a molded article of theinvention.

[0046]FIG. 11 is a typical perspective view of another example of a gatelayout of hot-runner sprues different from the gate layout shown in FIG.10.

[0047]FIG. 12 is a typical perspective view of another example of a gatelayout of hot-runner sprues different from the gate layout shown in FIG.10.

[0048]FIG. 1A is a plan view of a housing as an example of a moldedarticle of the invention.

[0049]FIG. 13B is a side view of the housing shown in FIG. 13A.

[0050]FIG. 14 is an illustration for explaining a method of measuringwarping of a molded article of the invention. The top drawing is a planview of the molded article and the bottom drawing is a front view of it.

[0051]FIG. 15 is an illustration showing the gate layout used inExample 1. The top drawing is a plan view of the gate layout and thebottom drawing is a vertical sectional view at the A-A position shown inthe plan view.

[0052]FIG. 16 is a typical vertical sectional view of the mold sectionin the hot-runner injection molding apparatus used in Examples 1 through10.

[0053]FIG. 17 is a vertical sectional detail view of the tip portion ofone of the hot-runner sprues shown in FIG. 16.

[0054]FIG. 18 is an illustration of the gate layout used in Example 2.The top drawing is a plan view of the gate layout and the bottom drawingis the vertical sectional view of it at the A-A position shown in theplan view.

[0055]FIG. 19 is an illustration of the gate layout used in Example 3.The top drawing shows a plan view of the gate layout and the bottomdrawing shows the vertical sectional view of it at the A-A positionshown in the plan view.

[0056]FIG. 20 is an illustration of the gate layout used in Example 4.The top drawing shows a plan view of the gate layout and the bottomdrawing shows the vertical sectional view of it at the A-A positionshown in the plan view.

[0057]FIG. 21 is an illustration showing the gate layout used in Example5. The top drawing shows a plan view of the gate layout, and the bottomdrawing, the vertical sectional view at the A-A position shown in theplan view.

[0058]FIG. 22 is an illustration of the gate layout used in Example 6.The top drawing shows a plan view of the gate layout and the bottomdrawing shows the vertical sectional view of it at the A-A positionshown in the plan view.

[0059]FIG. 23 is an illustration of the gate layout used in Example 7.The top drawing shows a plan view of the gate layout and the bottomdrawing shows the vertical sectional view of it at the A-A positionshown in the plan view.

[0060]FIG. 24 is an illustration of the gate layout used in Example 8.The top drawing shows a plan view of the gate layout and the bottomdrawing shows the vertical sectional view of it at the A-A positionshown in the plan view.

[0061]FIG. 25 is an illustration of the gate layout used in Example 9.The top drawing shows a plan view of the gate layout and the bottomdrawing shows the vertical sectional view of it at the A-A positionshown in the plan view.

[0062]FIG. 26 is a typical plan view for illustrating the resin passagesin the hot-runner manifold used in Example 9.

[0063]FIG. 27 is an illustration of the gate layout used in Example 10.The top drawing is a plan view of the gate layout and the bottom drawingis a vertical sectional view of it at the A-A position shown in the planview.

[0064]FIG. 28 is an illustration of the gate layout of the conventionalcold-runner injection molding apparatus used in Comparative Example 1.The top drawing is a plan view of the gate layout and the bottom drawingis a vertical sectional view of it at the A-A position shown in the planview.

[0065]FIG. 29 is a typical vertical sectional view showing the moldsection in the cold-runner injection molding apparatus used inComparative Example 1.

[0066]FIG. 30A is a perspective view of an example of a depressionportion formed by a hot-runner gate portion on a surface of a moldedarticle of the invention.

[0067]FIG. 30B is a vertical sectional view of the depression portionshown in FIG. 30A.

[0068]FIG. 31 is an illustration of the gate layout used in Example 12.The top drawing is a plan view of the gate layout and the bottom drawingis a vertical sectional view of it at the A-A position shown in the planview.

[0069]FIGS. 32A, 32B and 32C are plan views for illustrating opening andclosing timings of the respective gates of hot runners used forproducing a molded article of the invention.

[0070]FIG. 33A is a plan view of an example of a molded article shape(mold design) for preventing an inward inclination of lateral faces of amolded article of the invention.

[0071]FIG. 33B is a front view of the molded article shape (mold design)shown in FIG. 33A.

[0072]FIG. 33C is a front detail view of an end portion of the moldedarticle shape (mold design) shown in FIG. 33B.

[0073]FIG. 34 is an illustration of the gate layout used in Example 11.The top drawing shows a plan view of the gate layout and the bottomdrawing is a vertical sectional view of it at the A-A position shown inthe plan view.

[0074]FIG. 35 is an illustration of the gate layout used in Example 13.The top drawing shows a plan view of the gate layout and the bottomdrawing is a vertical sectional view of it at the A-A position shown inthe plan view.

[0075]FIG. 36 is an illustration of the gate layout used in Example 14.The top drawing shows a plan view of the gate layout and the bottomdrawing is a vertical sectional view of it at the A-A position shown inthe plan view.

[0076]FIG. 37 is a vertical sectional view of an example of the valvepin, guide and gate bush in one of the hot runners used for producing amolded article of the invention.

THE BEST MODES FOR CARRYING OUT THE INVENTION

[0077] A thermoplastic resin used for producing an FRP molded article ofthe invention is not especially limited if it can be injection-molded. Apolyamide resin or a polycarbonate resin can be preferably used.

[0078] The polyamide resin refers to a compound having an acid amidebond (—CONH—) bond in the molecule. Examples of the polyamide resininclude homopolymers and copolymers obtained from ε-caprolactam,6-aminocaproic acid, (ω-enantholactam, 7-aminoheptanoic acid,11-aminoundecanoic acid, 9-aminononanoic acid, α-pyrrolidone,α-pyrelidone, etc., homopolymers and copolymers obtained bypolycondensing a diamine such as hexamethylenediamine,nonamethylenediamine, undecamethylenediamine, dodecamethylenediamine ormetaxylylenediamine and a dicarboxylic acid such as terephthalic acid,isophthalic acid, adipic acid or sebacic acid, and their blends.

[0079] In view of the mechanical properties and surface properties ofthe molded article, 6-nylon and 66-nylon can be preferably used, andespecially 6-nylon can be preferably used.

[0080] The polyamide resin can also be mixed with another resin.Examples of the resin that can be mixed include polypropylene, ABSresin, polyphenylene oxide, polycarbonates, polyethylene terephthalate,polybutylene terephthalate, liquid crystal polyesters, etc.

[0081] In the case where a polymer having, for example, an esterreactive with a polyamide is mixed, the polyamide can be made to reactwith, for example, an acid anhydride beforehand for blocking the ends ofthe polyamide, in order to inhibit the reaction as required.

[0082] A polyamide resin has very high toughness and excellentmechanical strength.

[0083] A polycarbonate resin is a polyester represented by the followingformula and obtained from carbonic acid and a glycol or dihydric phenol.

[0084] Formula: —(—O—R—O CO—)_(n)— (R: a divalent aliphatic or aromaticgroup)

[0085] It is preferred that R is a diphenyl alkane having a structurerepresented by the following formula, since a high melting point, andexcellent heat resistance, light resistance, acid resistance, etc. canbe obtained.

[0086] Formula: —Ar—CR′R″—Ar— (Ar: a benzene ring, R′, R″: H, CH₃, C₂H₅)

[0087] Especially a polycarbonate having 2,2-bis(4-oxyphenyl)propanerepresented by the following formula is preferred.

[0088] Formula: —(—O—Ar—CMe₂—Ar—O—CO—)_(n)— (Me: a methyl group)

[0089] The hydrogen atoms, etc. of the polycarbonate can also besubstituted by halogens, hydrocarbon groups, etc.

[0090] The polycarbonate resin can be as it is, or can also be providedas an adequate alloy.

[0091] A polycarbonate/ABS (acrylonitrile-butadiene-styrene) (apreferred mixing ratio by weight is 20/80 to 80/20, and a more preferredratio is 40/60 to 60/40), a polycarbonate/ASA(acrylonitrile-styrene-acryl rubber) (a preferred mixing ratio by weightis 20/80 to 80/20, and a more preferred ratio is 40/60 to 60/40), analloy with another resin, a mixture with another resin, etc. can also bepreferably used.

[0092] A polycarbonate resin has low shrinkage and excellent warpingresistance.

[0093] Thermoplastic resins other than polyamide resins andpolycarbonate resins include polyolefin resins such as styrene resin,polyethylene and polypropylene, polyester resins such as polyphenyleneether resin, polyethylene terephthalate (PET) and polybutyleneterephthalate (PBT), etc.

[0094] Any one of these thermoplastic resins can be used or some of themcan also be used as a mixture or copolymer. In the case of a mixture, acompatibilizing agent can also be used together.

[0095] A flame retarder such as bromine flame retarder, silicone flameretarder or red phosphorus can also be added. A phosphoric ester orcarbon black can also be added.

[0096] In the case where a mixture consisting of plural resins is usedas the thermoplastic resin, it is preferred that a polyamide resin orpolycarbonate resin is a main ingredient, and that the content of themain ingredient is 60 wt % or more.

[0097] The mixture can also contain 0.1 to 10 wt % of a flame retarderor 0.1 to 30 wt % of carbon black, etc.

[0098] Depending on the application of the molded article, for example,a dye, pigment, moldability improving agent and foaming agent can beadded.

[0099] It is preferred that the molded article contains 30 to 95 wt % ofa thermoplastic resin. A more preferred range is 40 to 90 wt %. If theamount of the thermoplastic resin is smaller than the range, theflowability during molding becomes low since the amount of the resin istoo small. If the amount is larger than the range, the effect ofreinforcing fibers becomes small since the amount of the resin is toolarge.

[0100] The reinforcing fibers used in the FRP molded article of theinvention can be glass fibers, carbon fibers, aramid fibers, etc.

[0101] In view of the bending properties and strength of the moldedarticle, it is preferred that the tensile modulus of elasticity of thereinforcing fibers themselves is 10,000 to 50,000 kgf/mm². A morepreferred range is 20,000 to 30,000 kgf/mm². Similarly it is preferredthat the tensile strength of the reinforcing fibers themselves is 200 to600 kgf/mm². A more preferred range is 300 to 550 kgf/mm².

[0102] In view of moldability, property exhibition rate, etc., it ispreferred that the molded article contain 5 to 30 wt % of reinforcingfibers. A more preferred range is 15 to 30 wt %.

[0103] To satisfy the electromagnetic wave shielding capability, it isimportant and most effective to decrease the volume resistivity of themolded article. For this purpose, it is preferred that the volumeresistivity of the molded article is 0.0001 to 0.01 Ω·m.

[0104] To improve the mechanical properties such as thermal conductivityand coefficient of linear thermal expansion of the molded article and todecrease the volume resistivity of the molded product, it is preferredto use carbon fibers as reinforcing fibers.

[0105] It is preferred that the density of carbon fibers is 1.70 to1.95. A more preferred range is 1.76 to 1.85. It is preferred that thediameter of a single carbon fiber is 5 to 8 μn, and a more preferredrange is 6.5 to 7.5 μm.

[0106] In the production of the molded article of the invention, afiller can be used. Examples of the filler include wollastonite,sepiolite, potassium titanate, xonotlite, phosphate fibers, dawsonite,gypsum fibers, molybdenum sulfide (MOS), aluminum borate, needle-likecalcium carbonate, tetrapod type zinc oxide, silicon carbide, siliconnitride, vapor phase epitaxial carbon fibers, magnesium hydroxide,aluminum hydroxide, basic magnesium sulfate and their combinations.

[0107] The wollastonite, sepiolite, potassium titanate, xonotlite,phosphate fibers, dawsonite, gypsumfibers, MOS, aluminum borate,needle-like calcium carbonate, tetrapod type zinc oxide, siliconcarbide, silicon nitride, vapor phase epitaxial carbon fibers, magnesiumhydroxide, aluminum hydroxides and basic magnesium sulfate can also becovered with carbon or treated with a silane coupling agent, etc. on thesurface, or these covered or treated fillers can also be used incombination.

[0108] In view of moldability into the molded article and the appearanceof the molded article, wollastonite, sepiolite and potassium titanateare preferred, and in view of exhibition of respective properties suchas warping resistance, stiffness and strength of the molded article,potassium titanate (K₂O.nTi₂) (n=1, 2, 6, 8; n=8 is especiallypreferred) is more preferred.

[0109] Apart from said potassium titanate, a needle-like filler in anyof various modes of titanium element can be used. Titanium as metal canalso be used, but a titanium compound obtained by combining it withanother element is preferred. As the titanium compound, a titanium oxideor a compound relevant to it is preferred. Preferred titanium compoundsare NaTi₆O₁₃ and Rb₂Ti₆O₁₃, though not especially limited to them.

[0110] As the titanium oxide, spherical or lumpy titanium oxideparticles are generally used as a colorant. In the invention, thewarping-reducing effect of the titanium oxide is used for reducing thewarping of the molded article.

[0111] As the particle shape of the filler contained in the moldedarticle, needles, lumps or flakes can be used. Among them, needles arepreferred, and it is preferred that the fiber length is 1 to 500 μm. Afiller having a fiber length of 5 to 100 μm is more preferred, and afurther more preferred range is 10 to 20 μm.

[0112] The needle-like filler contained in the molded article can bepre-compounded in the resin or a flaky filler can also be blended in thepellets.

[0113] It is preferred that the filter content of the molded article is0 to 40 wt %. In the case of a needle-like filler, considering theinfluence on moldability, etc., it is preferred that the content is 1 to25 wt %, and a more preferred range is 5 to 20 wt %.

[0114] It is preferred that the aspect ratio (fiber length/fiberdiameter) of the needle-like filler is 3 to 500, and a more preferredrange is 5 to 400. A further more preferred range is 10 to 200.

[0115] The needle-like filler can be treated on the surfaces of theneedles with any of various treatments. For example, a needle-likefiller covered with carbon or tin oxide by means of chemical vapordeposition (CVD) can be used. To impart electric conductivity, aneedle-like filler covered on the surfaces of the needles with any ofvarious metals such as silver, nickel and copper by means of CVD orplating-can be used.

[0116] To improve the adhesiveness to the polyamide resin, a fillertreated on the surfaces of its particles with, for example, a silanecoupling agent can be used. Both covering and coupling agent treatmentcan also be used together.

[0117] These materials with various features can be used as required,considering the properties of the FRP molded article of the inventionand the characteristics of the process for producing the FRP moldedarticle.

[0118] A molded material can be used as it is as a molded article, orthe molded material can be finely reground and molded again into amolded article to be used. The reground material can also be afrequently reused one. Into a material not ground at all (virginmaterial), a certain amount of said ground material can also be addedfor use.

[0119] In this case, it is preferred that the mixing rate of thereground material into the virgin material is 0 to 50 wt %, in view ofnot extremely lowering the mechanical properties of the molded article.It is especially preferred that the rate is 0 to 40 wt % in view of notextremely lowering the impact resistance, and a range of 0 to 25 wt % ispreferred for maintaining the flame retardancy.

[0120] Hitherto, it is feared that in the case where a molded articleshaped like a polyhedral box has an opening, it may be warped if thematerial of the molded article is an engineering plastic such aspolyamide resin or polycarbonate resin or a material with reinforcingfibers added to the plastic, since there is no facial form for keepingthe stiffness.

[0121] However, in the FRP molded article of the invention, since a finefiller, especially preferably a needle-like filler is used, localmolding shrinkage and irregular stiffness can be inhibited, and as aresult, even if the housing obtained as the molded article has anopening, the warping of the housing can be kept small.

[0122] A preferred FRP molded article of the invention can be producedif pellets for injection molding containing a thermoplastic resin,reinforcing fibers and filler are injection-molded, with such conditionsas mold structure, resin molding temperature, injection pressure,holding pressure and mold cooling time in a hot-runner injection moldingapparatus adequately selected.

[0123] In this case, it is preferred that the average fiber length ofthe reinforcing fibers is 0.1 to 7 mm, and that the typical wallthickness of the molded article is in a range of 0.2 to 5 mm. Underthese conditions, excellent moldability into a thin-walled moldedarticle can be exhibited.

[0124] If the average length of the fibers in the molded article is lessthan 0.1 mm, the mechanical properties (such as bending modulus ofelasticity and tensile strength) of the molded article decline. If themolded article is required to have high stiffness, fibers having alonger average fiber length are more advantageous. It is preferred thatthe average fiber length in this case is 0.2 mm or more. More preferredis 0.3 mm or more.

[0125] On the other hand, if the average length of fibers in the moldedarticle is more than 7 mm, it is feared that the fibers are irregularlydispersed to exist in the molded article, though a large reinforcingfiber effect can be expected. The irregular dispersion of fibers resultsin molded articles irregular in appearance and mechanical strength,making it difficult to achieve stable production and stable yield.

[0126] Therefore, considering the above, it is preferred that theadequate length of fibers in the molded article is 0.1 to 7 mm in viewof sustaining stable production and stable yield. In view of sustaininghigh stiffness and impact resistance, it is more preferred that thelength is 0.2 mm to 7 mm, and a further more preferred range is 0.3 mmto 7 mm.

[0127] Suitable outside dimensions of the molded article are about 10 toabout 5,000 mm in length, about 10 to about 5,000 mm in width and about0.2 to about 1,000 mm in height.

[0128] Preferred is an injection-molded resin article having outsidedimensions of about 10 to about 500 mm in length, about 100 to 1,000 inwidth and about 0.2 to about 100 mm in height, and having at least onerib having a height of about 1 to 100 mm, a width of about 0.1 to about5 mm and a length of about 1 to about 1,000 mm, or having at least oneboss having a height of about 1 to about 100 mm and an outer diameter ofabout 1 to about 50 mm., More preferred is an injection-molded resinarticle having outside dimensions of about 50 to 300 mm in length (morepreferred is about 100 to about 300 mm in length), about 100 to about400 mm in width and about 0.2 to about 50 mm in height, and having atleast one rib having a height of about 1 to about 50 mm, a width ofabout 0.1 to about 5 mm and a length of about 1 to 400 mm, or having atleast one boss having a height of about 1 to about 50 mm and an outerdiameter of about 1 to about 50 mm.

[0129] In the case where it is difficult to arrange reinforcing fibersin the small spaces of a thin-walled molded article having a rib or bosswhen the reinforcing fibers are long, a fine filler, especiallypreferably a needle-like filler can be used to fill the small spaces andto inhibit local molding shrinkage and irregular stiffness, and as aresult, the molded article produced can be less warped and has highmechanical strength.

[0130] It is preferred that the bending modulus of elasticity of themolded article is 500 to 4,000 kgf/mm², and that the volume resistivityof the molded article is 0.001 to 0.01 Ω·m.

[0131] The molded article can be produced if thermoplastic resin pelletscontaining 5 to 50 wt % of reinforcing fibers having an average fiberlength of 0.1 mm or more and 0.01 to 30 wt % of a needle-like fillerselected from wollastonite, sepiolite, potassium titanate, xonotlite,phosphate fibers, dawsonite, gypsum fibers, MOS, aluminum borate,needle-like calcium carbonate, tetrapod type zinc oxide, siliconcarbide, silicon nitride, vapor phase epitaxial carbon fibers, magnesiumhydroxide, aluminum hydroxides, basic magnesium sulfate and theircombinations are supplied into a hot-runner injection molding apparatus.

[0132] In this case, it is preferred that the aspect ratio of theneedle-like filler is 3 to 500.

[0133] The molded article can also be covered on the surface with carbonor treated on the surface with a silane coupling agent.

[0134] In the invention, a housing refers to a container for containingan article, or a shell structure portion covering the functionalelements of an article, or a whole of an article including the inside.Examples of the article include precision electronic apparatuses anddevices such as a personal computer, desk-top calculator, controller,electronic measuring instrument, communication device, printer and imagescanner, portable electronic devices, portable cellular phone and largeplasma display panel (PDP) and chassis. The housing preferably used isrectangular. It can be preferably used as a housing of a personalcomputer, especially notebook type personal computer.

[0135] It is preferred that the housing as the FRP molded article of theinvention is a polyhedral box in visual shape. The polyhedron istypically a rectangle, though not limited to it. The polyhedron can alsobe a non-rectangle, for example, having a non-right-angled portion asthe angle formed between sides, or a trapezoid or parallelogram. It isnot necessary that all the faces are flat, and at least one face may becurved (convex or concave).

[0136] The form of the opening or the rate of the opening in the housingcan be selected variously depending on the desired housing shape, butfor inserting contents into the housing, it is preferred that an openingis formed at least in one face of the polyhedron. Typically it ispreferred that one face as a whole is substantially entirely open. Inaddition to the opening, one or more openings smaller than it can existin another face or other faces.

[0137] The FRP molded article of the invention can have electricconductivity, or can have a decorative effect, or can have a protectivelayer formed on the surface. In this case, the molded article is coveredwith a plating material or coating material.

[0138] The materials that can be plated on the surface include Au, Ag,Cu, Cr, Pt, Ni, Ti, Ge, Sn, Mo, Ta, W, Al, Nb, Pd, ITM, Inconel, Ni—Cr,426 gold, Permalloy, SiO, SiO₂, Cr₂O₃, Al₂O₃, SnO, SnO₂, ZrO₂, TiO₂,Ta₂O₅, BaTiO₃, Fe₂O₃, Y₂O₃, CaF₂, LiF, MgF₂, NbF₃, Si₃N₄, 7059 TiN,Sn—Sb, Si, Al+Si, SUS 304, etc.

[0139] The coating on the surface is selected depending on the color,look and taste required for the product. The molded article can becoated simply to have a decorative effect, and also coated with anelectrically conductive coating material, to be improved in electricconductivity.

[0140] The hot-runner injection molding apparatus used for producing theFRP molded article of the invention is described below.

[0141] In FIG. 1, a hot-runner injection molding apparatus 1 is composedof a molten resin extruder 3 installed on a base 1 c, a fixed body 1 battached to the tip of the molten resin extruder 3, a movable body 1 ainstalled on the base 1 c, to oppose the fixed body 1 b accessibly toand leavably from the fixed body 1 b, a fixed side plate 4 attached tothe fixed body 1 b, a movable side plate 5 attached to the movable body1 a, and a mold 2 supported by the fixed side plate 4 and the movableside plate 5 and positioned between them. The mechanism for moving themovable body 1 a is not illustrated.

[0142]FIG. 2 shows the detail of the fixed side plate 4, the mold 2 andthe movable side plate 5 of the hot-runner injection molding apparatus 1shown in FIG. 1. In FIG. 2, the cavity 6 of the mold 2 is attached tothe fixed side plate 4 and the core 7 of the mold 2 is attached to themovable side plate 5. When the opposite faces of the cavity 6 and thecore 7 contact each other, a mold hollow section 11 is formed.

[0143] Inside the fixed side plate 4 and the cavity 6, provided are afirst sprue 10 for receiving the stream of the molten resin fed from themolten resin extruder 3, a hot-runner manifold 9 for receiving thestream of the molten resin fed from the first sprue 10, and pluralhot-runner sprues 8 for receiving the respective streams of the moltenresin branching and fed from the hot-runner manifold 9.

[0144] At the ends downstream of the respective hot-runner sprues 8,gate portions (not illustrated) are provided, and when the gate portionsare opened, the respective hot-runner sprues 8 inject the molten resinfrom the gate portions into the mold hollow section 11.

[0145] The first sprue 10, the hot-runner manifold 9 and the hot-runnersprues 8 keep the resin always molten at a high temperature, unlike thecase of cold-runner injection molding. For this purpose, the first sprue10, the hot-runner manifold 9 and the hot-runner sprues 8 are providedwith an electric heater respectively. Also at the tip portions of thehot-runner sprues 8, an electric heater is provided respectively. Thesemeans keep the resin always molten.

[0146]FIG. 37 shows an example of the hot-runner sprue 8. In FIG. 37,the hot-runner sprue 8 has a hollow section 80 for allowing the resin toflow in it, and a molten resin passage 37 communicating to the moltenresin passage of the hot-runner manifold 9 and to the hollow section 80.The tip of the hollow section 80 is opened at the tip of the hot-runnersprue 8. Covering the opening at the tip, a sprue bush 22 is installedat the tip of the hot-runner sprue 8, to form a gate portion 14. Thesprue bush 22 has a gate hole 14 a formed. The hot-runner sprue 8 has agate pin 15 inserted into the hollow section 80 from outside andreaching the gate hole 14 a. The gate pin 15 is supported by means of aguide 36 movably in the axial direction. At the end of the gate pin 15on the side opposite to the tip portion, a gate pin drive means 15 b isprovided. The tip portion of the gate pin 15 and the gate hole 14 aconstitute a gate. When the tip portion of the gate pin 15 opens andcloses the gate hole 14 a, the molten resin is injected and theinjection is stopped.

[0147]FIG. 3 shows the hot runner sprue 8 and the hot-runner manifold 9.As shown in FIG. 3, the length of the hot runner sprue 8 is defined asthe length L from the downstream end of the hot-runner manifold 9 to thedownstream end of the gate portion 14 of the hot-runner sprue 8.

[0148] The length L of the hot-runner sprue 8 is selected depending onthe shape of the article to be molded and the size of the mold used formolding. When the FRP molded article of the invention is produced, it ispreferred that the length L of the hot-runner sprue 8 is 10 to 600 mm. Amore preferred range is 100 to 450 mm.

[0149] If the length L of the hot-runner sprue 8 is too short, thedistance between the manifold 9 and the tip portion of the hot-runnersprue 8 becomes too small, and the space where an external heat sourceof the hot-runner sprue 8 is disposed becomes small, making it difficultto adequately heat the hot-runner sprue 8.

[0150] If the length L of the hot-runner sprue 8 is too long, the lengthof the gate pin 15 for valve gate control for opening and closing thegate of the hot-runner sprue 8 becomes too long, making it difficult tocontrol the movement of the gate pin 15. Furthermore, the frictionbetween the gate hole 14 a and the gate pin 15 at the tip portion of thegate portion 14 becomes large, and the gate pin 15 or the gate hole 14 ais likely to be worn.

[0151]FIG. 4 is a vertical sectional view of the hot-runner sprue 8. Thehot-runner sprue 8 has a resin passage 12 formed inside by the hollowsection 80, and has the gate portion 14 at the tip portion. It ispreferred that the diameter of the gate hole 14 a of the gate portion 14is 0.1 to 10 mm for producing the molded article of the invention. Amore preferred range is 1 to 5 mm.

[0152] If the diameter of the gate hole 14 a is too large, thereinforcing fibers are insufficiently dispersed into the resin, causingthe obtained molded article to be poor in appearance. If the hole of thegate hole 14 a is too small, the resin cannot be sufficiently keptflowing, and flow defects such as short shots occur.

[0153] The hot-runner sprue 8 can be heated externally as shown in FIG.4 or internally. Both the heating methods have an advantage and adisadvantage respectively. In the production of the FRP molded articleof the invention, since reinforcing fibers are used together with athermoplastic resin, it is preferred to heat the hot-runner sprue 8externally.

[0154] When the hot-runner sprue 8 is heated internally, a heatingsource is installed inside the hot-runner sprue. So, it cannot beensured that all the resin in the hot-runner sprue is kept molten, andit becomes difficult to keep the runner passage diameter (flow rate ofresin) always substantially constant. Especially in the case wherecarbon fibers are used as the reinforcing fibers, since the heatconduction of carbon fibers is very good, the resin in contact with thelateral face of the hot-runner sprue is solidified, making it difficultto ensure the desired runner passage diameter (flow rate of resin). Ifit becomes difficult to ensure the desired runner passage diameter (flowrate of resin), it becomes difficult to keep the resin flow balanced,and the obtained molded article is likely to be warped or has poorappearance.

[0155] The hot-runner sprue 8 to be externally heated has an electricwire heater 13 a (FIG. 4) as a heat source outside the hot-runner sprue8. The resin in the resin passage 12 in the hot-runner sprue 8 isperfectly kept molten.

[0156] It is preferred that a heater (not illustrated) for local heatingis disposed at the gate portion 14 of the hot-runner sprue 8. Since thegate portion 14 of the hot-runner sprue 8 is always kept in contact withoutside air and the mold 2, the temperature of the resin positioned atthe gate portion 14 is likely to decline, and as the case may be, it canhappen that the resin is solidified at the gate portion 14, not allowinginjection molding. This problem can be avoided if a heater for localheating is disposed at the gate portion 14.

[0157] In reference to FIGS. 5A and 5B, the actions of opening andclosing the gate portion 14 of the hot-runner sprue 8 are describedbelow. It is preferred that the gate portion 14 of the hot-runner sprue8 in the hot-runner injection molding apparatus for producing the FRPmolded article of the invention is controlled using a valve.

[0158] The method of controlling a gate using a valve is called a valvegate method. In this method, when the resin is injected, the gate pin 15recedes from inside the gate portion 14 as indicated by arrow 15 a, toopen the gate portion 14. As a result, the resin passage at the gateportion 14 is opened, allowing the resin to be injected into the moldhollow section 11. After the resin has sufficiently filled the moldhollow section 11, the gate pin 15 advances as indicated by arrow 15 b,to close the gate portion 14. As a result, the resin passage at the gateportion 14 is closed to stop the injection of the resin into the moldhollow section 11.

[0159] That is, the gate pin 15 controls the injection of the resin andthe stop of the injection. In the case where there is only onehot-runner sprue 8, only one gate pin 15 control system is needed.

[0160] On the other hand, in the production of the molded article ofthe, invention, there arise a case where several hot-runner sprues 8become necessary, though depending on the size of the molded article.For example, when the housing of an office machine or device, especiallyof an A4 size (width 210 mm, length 297 mm) notebook type personalcomputer is produced using a hot-runner injection molding apparatus, 1to 26 gates can be used. However, it is preferred that the number ofgates is 4 to 17.

[0161] If the number of gates is too small, the resin cannot besufficiently kept flowing, and short shots occur, not allowing desiredmolded articles to be obtained. If the number of gates is too large, itbecomes difficult to dispose hot-runner sprues as many as the gates.

[0162] In the case where many hot-runner sprues are used for producingone molded article, it is preferred to control the opening and closingof the gates for the respective hot-runner sprues independently. Thiscontrol method allows the quantities of the resin flowing into the moldfrom the respective gates to be equal to each other. If the quantitiesof the resin flowing into the mold from the respective gates are keptequal to each other, the warping peculiar to the molded article obtainedfrom a thermoplastic resin containing reinforcing fibers can be keptsmall.

[0163] It is preferred that the movement of the gate pin 15 iscontrolled by means of fluid pressure, more specifically oil pressure,air pressure or water pressure. Among them, oil pressure or air pressureis more preferred.

[0164] The valve control method is excellent in the fine adjustment ofgate opening and closing times and resin flow rate because of itscharacteristics, and the balance of injection flow rates can be easilycontrolled. As a result, a molded article substantially free fromwarping and excellent in appearance can be obtained.

[0165] In the case where a long fiber-reinforced resin isinjection-molded using the cold-runner injection molding method, thereinforcing fibers are separated from the resin at the gates where theresin flows into the cavity of the mold from the sprues, and the fiberdensity at the gates becomes high. So, when the mold is opened, aphenomenon that the portions of the molded article positioned at thegates are torn off is likely to occur.

[0166] This phenomenon relates to the shape of the gates (especially thediameter of the gate holes), and in the case of a resin containing longfibers, if the gate hole diameter is larger, the phenomenon occurrencefrequency becomes higher. To prevent the tearing off at the gates, themold shape is designed to avoid that the gates are not disposed directlyon the surface of the molded article, and the obtained molded articlemust be additionally processed at the portions corresponding to thegates. This raises the cost.

[0167] If a hot-runner system of valve gate method is used for producingthe molded article of the invention, the gates can be reliably closed bymeans of the valve pins disposed in the hot-runner sprues, and even ifthe gates are disposed directly on the surface of the molded article,the phenomenon of tearing off at the gates does not substantially occur.

[0168] In this case, pin marks are formed on the molded article asdepressions at the positions corresponding to the gates. An example ofthe depression is shown in FIGS. 30A and 30B. The depressed pin mark 31has a depth (DP) of 0.05 to 0.3 mm and a diameter (GD) equal to the holediameter of the gate used.

[0169] The hot-runner manifold 9 is heated by means of an externalheater (not illustrated) like the hot-runner sprues 8, to keep the resinmolten.

[0170] The outside shape of the hot-runner manifold 9 is depicted as abox in FIG. 2, but the manifold has a heater inside for heating theresin and has resin passages (runners) formed inside.

[0171] The outside shape of the hot-runner manifold 9 depends on thesize of the mold 2 used and the number of the hot-runner sprues 8. Forexample, in the case where the housing of an office machine or device,especially an A4 size notebook type personal computer is molded using ahot-runner injection molding apparatus, it is preferred that the outsideshape of the housing is a box having a length of about 100 to about 600mm, a width of about 100 to about 600 mm and a height of about 10 toabout 600 mm. It is more preferred that the box has a length of about200 to about 500 mm, a width of about 100 to about 500 mm and a heightof about 10 to about 500 mm. It is further more preferred that the boxhas a length of about 200 to about 400, a width of about 100 to about300 mm and a height of about 10 to about 400 mm.

[0172] It is preferred that the resin passages in the hot-runnermanifold 9 have an inner diameter of 1 to 30 mm. A more preferred rangeis 2 to 20 mm, and a further more preferred range is 2 to 15 mm.

[0173] The hot-runner manifold 9 generally has a horizontally splittablestructure or an integral structure. In the case of horizontallysplittable structure, the top and bottom members respectively havingrunner halves are joined, for example, by means of welding, adhesive,bolting, pinning, fitting or vibration fusion. The runners in theintegral structure can be formed by way of drilling holes from a lateralface.

[0174] In the hot-runner injection molding apparatus for producing theFRP molded article of the invention, the resin passage distances fromthe inlet at which the resin flows from the molten resin extrusionmolding machine 3 into the hot-runner manifold 9 (first sprue 10) to thegate portions 14 of the hot-runner sprues 8 opened to the mold hollowsection 11 of the mold 2 are as described below.

[0175] In the case where the FRP molded article of the invention isproduced with plural hot-runner gates, it is preferred that thedistances to the respective gates are substantially equal to each other.The distance to each gate is not a straight-line distance, but adistance during which the resin flows.

[0176] That distances are substantially equal to each other means thatit is preferred that the value of SL/SS is 3 or less, where SL is thelongest distance to a gate and SS is the shortest distance to a gate.More preferred is 2 or less, and further more preferred is 1.5 or less.

[0177] On the other hand, in the case where the distances cannot be madesubstantially equal to each other as described above due to the moldstructure, the same effect can be achieved if the opening and closingtimings of respective hot-runner gates are made different. Making theopening and closing timings different means that the respective gatesare opened and closed at different times.

[0178] The state achieved in this way, in which the distances to therespective gates are substantially equal to each other, is veryeffective for decreasing the warping of the obtained molded article.

[0179] The article obtained by injection-molding a fiber-reinforcedresin has anisotropy in the molded article as a whole due to theoriented reinforcing fibers, irrespectively of whether the resinconstituting most of the material is a crystalline resin or an amorphousresin. The molded article obtained by injection molding shrinks while itis cooled from the state where it is discharged from the mold (hightemperature), to room temperature. The shrinkage depends on thereinforcing fibers used and the orientations. In the case where athermoplastic resin containing reinforcing fibers is used, if the fibersappear to be uniformly oriented in the molded article, the warping ofthe molded article can be greatly decreased.

[0180] In the case where a thermoplastic resin containing reinforcingfibers is used, if the resin passage distances from the first sprue tothe respective gates are equal to each other, there is an effect thatthe warping of the obtained molded article can be kept small.

[0181] In the case where a fiber-reinforced resin is used, thereinforcing fibers are oriented radially from the gate concerned. In thecase where plural gates are used, the reinforcing fibers are orientedradially from the respective gates. The state of the radially orientedreinforcing fibers decides the warping in the obtained molded article.If the quantities of the resin inflow from the respective gate portionsare not equal to each other, the balance among the quantities of resininflow at the portions of the molded article corresponding to therespective gates is lost to increase the warping.

[0182] In the case where plural gates are used, if the distances to therespective gates are equal to each other, the quantities of resin inflowinto the portions of the molded article corresponding to the respectivegates become substantially equal to each other. So, the warping of theobtained molded article can be decreased, and furthermore, the resinpressure distribution occurring during injection molding becomesuniform.

[0183] For example, as shown in FIG. 26, for the gate portions 14relatively close to the first sprue 10 in straight-line distance, theresin passages 25 are formed as detours to ensure that the distances tothe respective gate portions 14 become substantially equal to eachother.

[0184] In the case where the FRP molded article of the invention has arectangular flat face of about A4 size, the hot-runner sprues 8 can bearranged to be vertically and horizontally symmetrical when viewed fromthe first sprue 10 side (when projected from the first sprue 10 side),or can also be vertically (in the short side direction) asymmetrical ornon-radial. If they are arranged to be horizontally (in the long sidedirection) asymmetrical, the balance among resin flow rates duringmolding is adversely affected, and the molded article will be greatlywarped.

[0185] In a thin-walled molded article having a vertical wall on alateral face, even if the distances to the respective gates aresubstantially equal to each other, or even if the distances to therespective gates are geometrically equal to each other, it can happenthat the molded article is greatly warped. The reason is that if thethickness of the top wall is thinner, the molded article is moreaffected by the vertical wall. In other words, the stiffness of the topwall becomes lower than that of the vertical wall, and the moldedarticle is likely to be affected by the orientations of reinforcingfibers. This problem that occurs also when the positions of weld linesare moved is described below in reference to an example.

[0186] In the case where plural gates are used for molding, the resinmasses flowing into the cavity in respectively different directionscollide with each other on the surface of the molded article, and weldlines are formed. The weld lines become an appearance defect of themolded article, depending on the coating employed.

[0187] In the production of the FRP molded article of the invention, thearrangement of the hot-runner sprues 8 is changed to move the positionsof weld lines, or one gate is used for molding to avoid the formation ofany weld line. In this case, since it can happen the molded article isgreatly warped, sufficient care must be exercised for gate arrangement.In the case where the use of one gate only is not possible and where itis difficult to move the positions of weld lines, or in the case therearises a coating problem even if the positions of weld lines can bemoved, it is necessary to arrange the gates not to be equal in distanceon purpose or to set the valve opening and closing timings to ensurethat the distances to the respective gates do not become equal to eachother on purpose.

[0188] In the case of an LCD cover of the housing for an A4 sizenotebook type personal computer, in the gate layout shown in FIG. 31, asshown in FIGS. 32A, 32B and 32C, if the gates 33 located in the centralportion (two gates are shown in the drawings) are opened to let theresin flow in from the gates 33 in the central portion about 0.1 to 2seconds after the resin has flowed in from the gates 32 located in theperipheral portion (four gates are shown in the drawings), a moldedarticle substantially not warped can be obtained.

[0189] As required, the gates 33 in the central portion opened later canalso be closed earlier than the gates 32 in the peripheral portion. Whatgates are selected for opening at a delayed timing and what time is setfor delayed opening can be decided variously depending on the shape ofthe molded article, mold structure and hot-runner manifold structure. Inthe case of an LCD cover of the housing for an A4 size notebook typepersonal computer, if the gates located in the peripheral portion areopened earlier and if the gates located in the central portion areopened a predetermined time later and closed, a desired molded articlecan be obtained effectively.

[0190] If the gates are arranged not to be equal to each other indistance on purpose or if the valve opening and closing timings are setto ensure that the distances to the respective gates do not become equalto each other, the height of the weld lines can be decreased. Decreasingthe height of weld lines means that the weld line height is actuallylowered, and that it cannot be observed that the weld lines exist.

[0191] An LCD cover, for example, an LCD cover of the housing for an A4size notebook type personal computer, contains an LCD panel inside. So,it is a hexahedron and generally the two faces of it have openings. Inthis case, for fixing the LCD panel on lateral faces of the housing,vertical walls are provided on the lateral faces. The vertical walls ofa molded article having the vertical walls on lateral faces, taken outof the mold, tend to incline inwardly due to material shrinkage. It isvery difficult to mount an LCD panel on the housing having inwardlyinclining vertical walls.

[0192] This problem can be solved by a method of correcting the inwardinclination of the lateral faces in the step of correcting the form ofthe molded article after coating. The problem can also be solved by amethod of designing a mold having lateral faces inclining outwardlybased on the predicted inward inclination of the lateral faces of theLCD cover.

[0193] This mode is shown in FIGS. 33A, 33B and 33C. FIG. 33A is a planview of the rear face of a molded article 20. FIG. 33B is the A-Avertical sectional view of FIG. 33A. FIG. 33C is an expanded verticalsectional view showing a lateral portion of the molded article 20. Inthese drawings, the molded article 20 has an outer surface 20TS and bothlateral faces 20SS.

[0194] In the case where a mold having lateral faces 20SS inclinedoutwardly (at an angle (Sθ)) is designed, it is preferred that theoutward inclination (EL) is EL=0.05 to 0.5 mm (Sθ=0.1 to 2.0°) for an A4size LCD cover (lateral face height 5 mm to 20 mm). A more preferredrange is EL=0.1 to 0.3 mm (Sθ=0.3 to 1.2°).

[0195] In this mode, it is assumed that the wall thickness of thelateral faces is not changed.

[0196] In the production of the FRP molded article of the invention, themold 2 used in the hot-runner injection molding apparatus isstructurally different from the generally used mold for resin injectionmolding, in the following constitution as shown in FIG. 6B.

[0197] The generally used mold for resin injection molding is made bymachining a lump of a steel material, and as shown in FIG. 6A, it iscomposed of such parts as a runner 27, a cavity 6 a, a core 7 a, etc.These parts have cooling water passages 13 b formed in them in astructure for cooling the respective parts by cooling water. A mold 2 ahas a structure capable of molding one to plural molded articles 20 a atone time of molding.

[0198] For producing the FRP molded article of the invention, in themold 2 used in the hot-runner injection molding apparatus, thehot-runner manifold 9, the hot-runner sprues 8 and the first sprue 10must keep the resin in molten state. So, the cavity 6, the core 7 andthe sprue bushes have high temperature portions and low temperatureportions. The low temperature portions have cooling water passages 13 bformed as in the generally used mold for resin injection molding, as astructure to cool the mold 2. On the other hand, the high temperatureportions have electric wire heaters 13 a (FIG. 7) for heating therespective parts, as a structure to keep the resin always in moltenstate.

[0199] The temperature of the mold as a cooled portion is about 20 to90° C., but the temperature of the hot-runner manifold 9, the hot-runnersprues 8 and the first sprue 10 as high temperature portions is about200 to 350° C.

[0200] It is preferred that the temperature of the mold in the cooledportions on the surfaces of the cavity 6 and the core 7 corresponding tothe surface of the molded article is about 20 to 90° C. A more preferredrange is about 30 to 85° C., and a further more preferred range is about30 to 80° C.

[0201] It is necessary to prevent that the heat of the high temperatureportions is transmitted to the low temperature portions, i.e., toinsulate heat between those portions. For the portion of the hot-runnermanifold 9, as shown in FIG. 7, an air heat insulating layer 17 isformed in the clearance between a low temperature portion and a hightemperature portion.

[0202] For the portions of the hot-runner sprues 8 and the first sprue10, a structure having more cooling water passages or having a largerpassage diameter compared with the generally used mold for resininjection molding is employed.

[0203] To keep the temperature of the surfaces of the cavity 6 and thecore 7 corresponding to the surface of the molded article at 20 to 90°C., a coolant fluid circulating mechanism is provided respectively onsaid surfaces or preferably in the gate bushes 22, or a coolant isbrought into contact with the surfaces whenever molding is carried out.As a further other method, a hollow heat insulating structure can beprovided respectively inside the surfaces. However, a method, in which aheat insulating plate 16 made of a heat insulating material is providedaround the gate portions 14 near the surfaces of the cavity 6 and thecore corresponding to the surface of the molded article, can bepreferably used.

[0204] As the material of the heat insulating plate 16, a materialhaving a large thermal capacity, i.e., a small thermal conductivity canbe used. Suitable materials having a small thermal conductivity for theheat insulating plate 16 include ceramics, antimony, iridium, carbonsteel, Ni—Cr alloy, silicon steel, stainless steel, nichrome, bismuthand titanium. Considering the strength and rigidity as mold steel, amongthem, carbon steel, Ni—Cr alloy, stainless steel and titanium arepreferred. Carbon steel, stainless steel and titanium are morepreferred. Any one of these metals can be used as required, or pluralmetals can also be used in combination. Any of these metals can also becombined with the mold material used.

[0205] The form of the heat insulating plate 16 is not especiallylimited. A plate having a polygonal or circular lateral side form issuitable, and in view of easy machinability, a circular plate is morepreferred. The heat insulating plate 16 can be installed for each gateas shown in FIG. 8, or can be installed for the entire surface of themold as shown in FIG. 7.

[0206] The size of the heat insulating plate 16 can be variously decideddepending on the size of the mold 2 and the size of the hot-runnersprues 8. For example, in the case where it is installed for each gate,it is preferred that the sectional area of the heat insulating plate is4 to 8,000 mm². A more preferred range is 15 to 5,100 mm², and a furthermore preferred range is 50 to 3,000 mm².

[0207] If the heat insulating plate is too large, it is difficult toinstall the heat insulating plate in view of the mold structure, and ifit is too small, the heat insulating effect cannot be expected.

[0208] The thickness of the heat insulating plate 16 is decided,considering the molten resin temperature and the thermal effect on themolded article. In the case where the heat insulating plate is installedfor each gate, it is preferred that the thickness is 0.1 to 20 mm. Amore preferred range is 1 to 15 mm, and a further more preferred rangeis 1.5 to 10 mm.

[0209] If the thickness is too large, the length of the pin 15 must belonger by a length corresponding to the thickness of the heat insulatingplate 16, and the length of the straight portion of the gate 14 becomeslonger, causing galling between the pin 15 and the gate 14. If thethickness is too small, the heat insulating effect cannot be expected,and the strength becomes insufficient. When the thickness of the heatinsulating plate 16 is not uniform, the average value is used as thethickness.

[0210] The heat insulating plate 16 can be composted of a metallic plateonly, or as shown in FIG. 9, it can also be a laminate consisting of ametallic plate 16 a and a plate 16 b made of another material such as aresin.

[0211] The gate portions 14 can be arranged directly on the surface ofthe molded article, but a heat insulating material 16 can be attached tothe tip portion of each gate.

[0212] In the case where a heat insulating material 16 cannot bearranged at the tip of each gate because of the mold structure, if thegate portion 14 is directly arranged on the surface of the moldedarticle, it can happen that the molded article becomes defective due toburn, etc., since the tip portion of the gate has a high temperature. Inthis case, between the gate portion 14 and the surface of the moldedarticle, a certain clearance can also be formed. In this case, themolded article has gate portions remaining, but if they are removed bymeans of machining, the same appearance as that obtained when the gateportions 14 are arranged directly on the surface of the molded articlecan be obtained.

[0213] The distance between the surface of the mold space and each gatecan be decided as required, but it is preferred that the distance is 0to 50 mm. A more preferred range is 0 to 30 mm, and a further morepreferred range is 0 to 10 mm. If this distance is too long, thepossibility of breaking the gate portion increases, and if it is broken,broken pieces remain in the mold after molding, necessitating thesuspension of the next molding. Furthermore, if this distance is toolong, since this portion is a portion not included in the molded article(portion to be thrown away), the waste increases to raise the cost ofthe molded article.

[0214] The materials that can be used to constitute the mold includecarbon steel for machine structure, chrome molybdenum steel, carbon toolsteel, alloy tool steel, high carbon bearing steel, aluminum chromemolybdenum steel, etc.

[0215] The gate layout is described below. To obtain a less-warpedmolded article excellent in appearance, the arrangement of thehot-runner sprues 8 is important.

[0216] In the case of a housing for an office machine or device typifiedby a housing for a notebook type personal computer, since the size isrelatively large, it is difficult to keep the resin flowable, and it ispreferred to arrange the gates on the face of the molded article.

[0217] As shown in FIG. 10, all the hot-runner sprues 8 can be arrangedon the face of the molded article 18, and as shown in FIG. 11, somehot-runner sprues 8 can be arranged on the face of the molded article 18while the other hot-runner sprues 8 are arranged at positions outsidethe face of the molded article 18. In the case of a polygonal moldedarticle having a large cutout portion as shown in FIG. 12, all thehot-runner sprues 8 can be arranged at positions outside the face of themolded article 18.

[0218] The mold structure is described below. An ordinary mold for resininjection molding is made by either the front gate method, in which thegates are mainly arranged on the decorative face of the molded article(surface of molded article), or the reverse gate method, in which thegates are not arranged on the decorative face of the molded article.

[0219] The mold used for producing the FRP molded article of theinvention can be made either by the front gate method or the reversegate method. Either method can be selected as required in response tothe appearance required for the molded article and the shape of themolded article.

[0220] For example, in the case where a molded article severe in theappearance standard of the decorative face like the housing foraccommodating the LCD panel for a notebook type personal computer isproduced, a mold that does not allow the gate form to appear on thedecorative face of the molded article is used. That is, in this case, amold made by the reverse gate method, in which the gates do not opposethe decorative face of the molded article, is used.

[0221] For a housing for accommodating, for example, an HDD for anotebook type personal computer or for producing a molded article usedas an internal part of an automobile or office machine, etc. which isnot required to be coated, the front gate method, in which the gates donot oppose the surface of the molded article, is employed since theappearance standard of the surface of the molded article is not sosevere as that for the housing for said LCD panel.

[0222] As described before, since the FRP molded article of theinvention is produced by means of hot-runner injection molding, thequantity of the sprue runners 19 (FIGS. 11 and 12) removed from theportion destined to be the product and thrown away is decreased.Furthermore, the molding cycle can be shortened.

[0223] In cold-runner injection molding, it is necessary to sufficientlycool both the portion destined to be the molded article and the spruerunner portions to be thrown away in the mold. If the sprue runnerportions are insufficiently cooled, a phenomenon that relatively thinsprue runner portions remain in the mold when the mold is opened occurs(sprue clogging phenomenon), and as the case may be, continuous moldingcannot be made. This phenomenon remarkably occurs in the molding using along fiber-reinforced resin material small in molding shrinkage comparedwith the general engineering plastics not containing reinforcing fibers.Therefore, the mold must be designed to suit the molding using a longfiber-reinforced resin material.

[0224] Since the FRP molded article of the invention is produced bymeans of hot-runner injection molding, the sprue runners existing in theconventional cold-runner injection molding do not exist in the mold.Therefore, the sprue clogging phenomenon does not occur.

[0225] The average fiber length in the FRP molded article of theinvention is a weight average fiber length. The measuring method is asfollows.

[0226] (i) A test piece having a size of 10 mm long×10 mm wide(thickness is not limited) is cut out of a molded article.

[0227] (ii) The test piece is immersed in a solvent for 24 hours, todissolve the resin component. As the solvent, a solvent capable ofdissolving the base resin of the molded article is selected adequately.For example, if the resin is nylon, formic acid can be selected. If theresin is a polycarbonate, dichloromethane or orthochlorophenol can beselected. After the resin portion of the test piece is dissolved, aninorganic substance including reinforcing fibers remains.

[0228] (iii) The reinforcing fibers are observed at a 10- to 100-foldmagnification using a microscope, and arbitrary 400 fibers among thereinforcing fibers within the field of view are selected for measurementof their lengths.

[0229] (iv) With the length of each fiber as Li, the weight averagefiber length Lw is obtained from the following formula.

[0230] Formula: L=(ÓLi²/ÓLi)

[0231] The FRP molded article of the invention can be produced by amethod of molding a resin containing long fibers having an average fiberlength of 0.1 to 7 mm. Therefore, the mold used and the parts combinedwith it and brought into contact with the flow of the resin are requiredto assure the desired dimensional accuracy of molded articles, to bedurable and to allow stable production of molded articles.

[0232] It is preferred that the surface hardness of the valve pin 15 andthe guide 36 (FIG. 37) is HRC45 to 68, considering wear resistance. Amore preferred range is HRC58 to 68. If the reinforcing fibers arecarbon fibers, a range of HRC60 to 68 is preferred.

[0233] It is preferred that the surface hardness of the gate bushes 22(FIG. 37) is HRC45 to 68, considering the wear resistance. A morepreferred range is HRC55 to 68.

[0234] The process for producing an FRP molded article of the inventionis described below more particularly.

[0235] The process for producing an FRP molded article of the invention,comprises (a) a first step, in which resin pellets havingresin-reinforcing fibers having an average fiber length of 0.1 to 7 mmmixed in a thermoplastic resin used as a matrix resin are heated andmolten at 220 to 350° C. in a resin-melting cylinder of an injectionmolding machine, to prepare a molten resin having the fibers dispersedto exist in it, and (b) a second step, in which the molten resinobtained in the first step is fed to a hot-runner sprue through a firstsprue of the injection molding machine and further through the resinpassage of a hot-runner injection molding apparatus; the gate of thehot-runner sprue is opened and closed to control the start and end ofinjection of the molten resin into the cavity of the mold used formolding an article; the molten resin fed into the cavity is solidifiedin the mold; the mold is opened; and the molded article is taken out.

[0236] As required, a third step of finishing the surface of the moldedarticle taken out of the mold at the portions corresponding to the gateportions, is added. As required, a fourth step of inserting metallicbits into the molded article taken out of the mold or the molded articleobtained from the third step is added.

[0237] As required, a fifth step of processing (sanding) the surface ofthe molded article to make the surface smooth is added after the secondstep, third step or fourth step.

[0238] As required, a sixth step of washing the surface of the moldedarticle and coating and drying the surface is added after the secondstep, third step, fourth step or fifth step.

[0239] As required, a seventh step of correcting the warping formed inthe molded article is added after the second step, third step, fourthstep, fifth step or sixth step.

[0240] As required, an eighth step of polishing the surface (includingthe coating surface) of the molded article is added after the secondstep, third step, fourth step, fifth step, sixth step or seventh step.

[0241] As required, a ninth step of inspecting the appearance andpacking the molded article is added after the second step, third step,fourth step, fifth step, sixth step, seventh step or eighth step.

[0242] The capacity of the hot-runner injection molding machine used forthe first step ranges from tens of tons to thousands of tons.The-capacity of the molding machine increases in proportion to thesurface area of the molded article to be produced. For example, in thecase where molded articles having a surface area of A4 size areproduced, it is preferred to use a hot-runner injection molding machinehaving a capacity of 350 tons or more.

[0243] It is preferred that the heating temperature set for the heaterinstalled in the cylinder of the hot-runner injection molding machine is220 to 350° C. In view of assuring the kneadability of the longfiber-reinforced resin and the sufficient flowability necessary forinjection molding, a more preferred range is 240 to-330° C. In the caseof a thermoplastic resin mainly composed of a polyamide resin, it ispreferred that the temperature is 240 to 320° C.

[0244] In the second step, the long fiber-reinforced thermoplastic resinmolten in the first step is made to flow into the mold cavity of thehot-runner injection molding apparatus. The quantity and timing of theinflow of the resin containing reinforcing fibers into the mold cavityare controlled by a method of opening and closing the valve pins in thehot-runner sprues.

[0245] To keep the resin always molten, the hot-runner manifold and thehot-runner sprues are kept at a high temperature. It is preferred thatthe temperature is set at 220 to 350° C. In view of the kneadability ofthe long fiber-reinforced resin and the sufficient flowability necessaryfor injection molding, a more preferred range is 240 to 330° C. In thecase where the thermoplastic resin is mainly composed of a polyamideresin, a preferred range is 240 to 320° C.

[0246] In the third step, the solidified molded article is taken out ofthe mold, and the surface is finished at the portions corresponding tothe gate portions. The portions of the hot-runner injection-moldedarticle corresponding to gates have depressions as valve pin marks.Whether or not the forms of the depressions conform to the appearancestandard of the molded article is judged, and based on the result,whether or not the molded article is processed in the third-step isdecided.

[0247] In the third step, usually, a machine tool having a rotary knifeis used to remove the forms of depressions, or the depressions arepacked with a thermoplastic resin, thermosetting resin, rubber or putty,etc.

[0248] In the fourth step, metallic bits are inserted into the moldedarticle. In general, the housing as the molded article accommodatesvarious functional parts in it. So, it is necessary to let the housinghave a threadably engaging mechanism. The engaging mechanism can beinstalled by thermally inserting metallic bits heated to a temperatureof about 280 to 320° C., into a boss, since the housing is-made of athermoplastic resin.

[0249] The engaging mechanism can also be installed without using thefourth step. A boss having holes smaller than the screw diameter isformed while the molded article is molded, and after completion ofmolding, self-tapping screws can be turned into the holes for threadingthem.

[0250] In the fifth step, the surface of the molded article is processedto be smooth (sanded). To obtain good appearance of coating, the surfaceof the molded article is processed to be smooth before coating. Forexample, a wet or dry processing method using sand paper or a processingmethod using a sandblaster can be used.

[0251] In the sixth step, the surface of the molded article is washed,coated as predetermined, and dried. For coating the molded articleobtained from a long fiber-reinforced thermoplastic resin, coatingmaterials of various colors and touches can be used.

[0252] In the seventh step, the warping of the molded article iscorrected. A long fiber-reinforced thermoplastic resin can be made intomolded articles of various shapes, and depending on the shape of themolded article, the tolerances of warping and torsion are narrow. Themolded article narrow in the tolerances of warping and torsion iscorrected in warping and torsion.

[0253] The correction is usually carried out by a method of fixing themolded article into a jig designed to obtain a desired shape, heatingthe molded article in this state for a certain time, and cooling. It ispreferred that the heating temperature is higher than the glasstransition temperature (Tg) and lower than the thermal deformationtemperature of the main resin of the molded article. It is preferredthat the temperature is 40 to 200° C., and a more preferred range is 50to 180° C. In the case where the main ingredient of the resin is apolyamide, it is preferred that the temperature is 70 to 140° C.

EXAMPLES

[0254] In Examples 1-15 and Comparative Example 1, the followingconditions were used.

[0255] The molded product produced in each example was an LCD panelhousing 20 for a notebook type personal computer shown in FIGS. 13A and13B. The panel 20 had a length (PL) of 310 mm, a width (PW) of 240 mmand a thickness (PT) of 15 mm. In one of the two sides in the lengthdirection, two depressions 201 and 202, each having a length (PLa) of 40mm and a width (PWa) of 10 mm, were formed.

[0256] The material of the pellets fed into the molten resin extruder 3used for producing the molded article 20 consisted of a polyamide resin(“Amilan” CM1004 produced by Toray Industries, Inc.), needle-likepotassium titanate filler (Tismo D produced by Otsuka Chemical Co.,Ltd.), and carbon fibers (“Torayca” T700S-12K-60E produced by TorayIndustries, Inc.). The material contained 1 wt % of the needle-likefiller and 20 wt % of the reinforcing fibers. Pellets were produced bymelt-molding the material into a linear molded article and cutting it ata length of 7 mm. The length of the reinforcing fibers contained in thepellets was substantially 7 mm.

[0257] As the molten resin extruder 3, JSW350-E2-SP was used. The resintemperatures in the cylinder were 260° C. (nozzle section), 270° C.(nozzle section), 280° C. (metering section), 280° C. (compressionsection), 270° C. (feed section) and 260° C. (feed section), in thedirection from the nozzle to the side of the hopper.

[0258] The resin temperature in the hot-runner manifold 9 (FIG. 2) was280° C., and the set temperature of the hot-runner sprues 8 was 270° C.Each of the hole diameter of the gate holes 14 a (FIG. 37) of thehot-runner sprues 8 was 1.5 mm. The material of the sprue bushes 22 wasHPM31.

[0259] The material of the cavity 6 and the core 7 of the mold 2 wasNAK60, and their surfaces were nitrided. The set temperature of the moldwas 50° C. at both the cavity 6 and the core 7.

[0260] On each of the molded articles 20 obtained in the respectiveexamples and comparative example, the amount of warping was measured.The measuring method is shown with FIG. 14, that is, the deviation fromthe straight line (BL) in the direction of the short axis (SA) of themolded article 20 (the thickness direction of the molded article 20)along the straight line in the direction of the central long axis (LA)of the molded article 20 was measured and thus obtained value was usedas the warping value (WA).

Example 1

[0261] As the hot-runner injection molding apparatus, SVP injectionmolding apparatus produced by Seiki Corp. was used as the base, and thelength of the hot-runner sprues 8 was 125 mm, while the hole diameter ofthe gate holes 14 a was 1.5 mm.

[0262] The hot-runner manifold 9 was a rectangle having a height of 150mm, a length of 340 mm and a width of 340 mm, and the inside resinpassages had a cross sectional form of a circle having a diameter of 8mm. The material of the hot-runner manifold 9 and the hot-runner sprues8 was SK3. The approximate vertical sections of the fixed side plate 4,the movable side plate 5, and the cavity 6 and the core 7 of the mold 2are shown in FIG. 16.

[0263] At one end face of the cavity 6, the first sprue 10 wasinstalled, and the first sprue 10 communicated to the hot-runnermanifold 9. At the tip of the hot-runner manifold 9, the hot-runnersprues 8 were provided. The tips of the hot-runner sprues 8 were openedinto the mold hollow section 21 through the gate pins 15. The moldhollow section 21 was formed between the cavity 6 and the core 7opposing the cavity 6. To the core 7, knockout pins 24 are attached. Inthe cavity 6, slide cores 23 were provided from its lateral faces towardthe mold hollow section 21. The apical angle (β) at the tip portions ofthe hot-runner sprues 8 was 80°.

[0264] The ratio of the longest resin passage (SL) to the shortest resinpassage (SS) among the resin passages in the hot-runner manifold 9 wasSL/SS=1.12.

[0265] The vertical sectional view at the tip of one of the hot-runnersprues 8 near the gate portion 14 is shown in FIG. 17. On the face ofthe gate portion 14 opposing the mold hollow section 21 of the mold 2,the heat insulating material 16 was provided. The heat insulatingmaterial 16 was made of stainless alloy PSL (produced by Hitachi Metals,Ltd.) and was a plate having a thickness of 3 mm and a diameter of 30mm, with a through hole having a diameter of 1.5 mm formed at thecenter.

[0266] In FIG. 17, the hot-runner sprue 8 had the hollow section 12having a diameter (SD) of 12 mm in the axial direction. The hollowsection 12 formed a resin passage, and the gate pin 15 was inserted intothe hollow section 12. The apical angle (α1) at the tip portion of thehollow section 12 was 65° C. The apical angle (α2) at the tip portion ofthe outside surface of the hot-runner sprue 8 was 80°. At the tipportion, the sprue bush 22 was provided, and the resin passage providedin the center of the sprue bush communicated, at one end, to the hollowsection 12, and, at the other end, to the gate portion 14. Around thehot-runner sprue 8, the heat insulating layer 17 with air contained init was formed.

[0267] The mold 2 was of the front gate method. The arrangement of sixhot-runner sprues 181 to 186 for the molded article 20 is shown in theplan view at top in FIG. 15. Since the respective gates of thehot-runner sprues 181, 184, 185 and 186 were located outside the face ofthe molded article 20, there existed sprue runners 19 to be thrown away.This mold 2 was used to produce molded article 20.

Example 2

[0268] The mold 2 was of the front gate method. The arrangement oftwelve hot-runner sprues 281 to 292 for the molded article 20 is shownin the plan view at top in FIG. 18. The mold 2 was used and the moldedarticle 20 was produced in the same manner described in Example 1.

Example 3

[0269] The mold 2 was of the front gate method. The arrangement offourteen hot-runner sprues 381 to 394 for the molded article 20 is shownin the plan view at top in FIG. 19. The mold 2 was used and the moldedarticle 20 was produced in the same manner described in Example 1.

Example 4

[0270] The mold 2 was of the front gate method. The arrangement ofseventeen hot-runner sprues 481 to 497 for the molded article 20 isshown in the plan view at top in FIG. 20. The mold 2 was used and themolded article 20 was produced in the same manner described in Example1.

Example 5

[0271] The mold 2 was of the front gate method. The arrangement ofthirteen hot-runner sprues 581 to 593 for the molded article 20 is shownin the plan view at top in FIG. 21. The mold 2 was used and the moldedarticle 20 was produced in the same manner described in Example 1.

Example 6

[0272] The mold was of the reverse gate method. The arrangement oftwelve hot-runner sprues 681 to 692 for the molded article 20 is shownin the plan view at top in FIG. 22. The mold 2 was used and the moldedarticle 20 was produced in the same manner described in Example 1.However, the length of the hot-runner sprues was set in 320 mm.

Example 7

[0273] The mold was of the reverse gate method. The arrangement offourteen hot-runner sprues 781 to 794 for the molded article. 20 isshown in the plan view at top in FIG. 23. The mold 2 was used and themolded article 20 was produced in the same manner described inExample 1. However, the length of the hot-runner sprues was set in 320mm.

Example 8

[0274] The mold was of the reverse gate method. The arrangement ofseventeen hot-runner sprues 881 to 897 for the molded article 20 isshown in the plan view at top in FIG. 24. The mold 2 was used and themolded article 20 was produced in the same manner described inExample 1. However, the length of the hot-runner sprues was set in 320mm.

Example 9

[0275] The mold was of the reverse gate method. The arrangement of sixhot-runner sprues 981 to 986 for the molded article 20 is shown in theplan view at top in FIG. 25. The mold 2 was used and the molded article20 was produced in the same manner described in Example 1. However, thelength of the hot-runner sprues was set in 320 mm. As in Example 1,since the respective gates of the hot-runner sprues 981, 982, 985 and986 were located outside the face of the molded article 20, thereexisted sprue runners 19 to be thrown away.

[0276]FIG. 26 shows the resin passages 25 from the first sprue 10 to therespective hot-runner sprues 981 to 986 in the hot-runner manifold 9used in this molding.

Example 10

[0277] The mold was of the reverse gate method. The arrangement ofthirteen hot-runner sprues 1081 to 1093 for the molded article 20 isshown in the plan view at top in FIG. 27. The mold 2 was used and themolded article 20 was produced in the same manner described inExample 1. However, the length of the hot-runner sprues was set in 220mm.

Example 11

[0278] The mold was of the reverse gate method. The arrangement of fivehot-runner sprues 1181 to 1185 for the molded article 20 is shown in theplan view at top in FIG. 34. The mold 2 was used and the molded article20 was produced in the same manner described in Example 1. However, thelength of the hot-runner sprues was set in 320 mm.

Example 12

[0279] The mold was of the reverse gate method. The arrangement of sixhot-runner sprues 1281 to 1286 for the molded article 20 is shown in theplan view at top in FIG. 31. The mold 2 was used and the molded article20 was produced in the same manner described in Example 1. However, thelength of the hot-runner sprues was set in 320 mm.

Example 13

[0280] The mold was of the reverse gate method. The arrangement of fivehot-runner sprues 1381 to 1385 for the molded article 20 is shown in theplan view at top in FIG. 35. The mold 2 was used and the molded article20 was produced in the same manner described in Example 1. However, thelength of the hot-runner sprues was set in 125 mm.

Example 14

[0281] The mold was of the reverse gate method. The arrangement of sixhot-runner sprues 1481 to 1486 for the molded article 20 is shown in theplan view at top in FIG. 36. The mold 2 was used and the molded article20 was produced in the same manner described in Example 1. However, thelength of the hot-runner sprues was set in 125 mm.

Comparative Example 1

[0282]FIG. 28 and 29 show the mold portion of a generally usedconventional cold-runner injection molding machine.

[0283] In FIG. 29, a mold 2 a comprises a cavity 6 a and a core 7 aopposing it, and in the core 7 a, slide cores 23 and knockout pins 24are provided. In the cavity 6 a, plural bushes 30 a are provided, and inthem, sprues 26 are respectively formed. The respective sprues 26communicate to the resin passage of a runner 27 provided outside thecavity 6 a. The resin passage communicates to the first sprue 28 formedin the bush 30 b provided in a fixed side plate 4 a. The first sprue 28communicates to a resin melting extruder (not illustrated). The length(TA) of the bushes 30 a is 220 mm, the thickness (TB) of the runner 27is 7 mm and the length (TC) of the bush 30 b is 50 mm. The apical angle(θ) at the tip portion of the sprue 26 is 12°.

[0284] The mold 2 a was of the reverse gate method. The arrangement ofeight sprues 261 to 268 for the molded article 21 is shown in the planview at top in FIG. 28. The mold 2 a was used and the molded article 21was produced in the same manner described in Example 1. In this molding,the resins in the sprues 261 to 268, the runner 27 and the first sprue28 were thrown away after molding every time.

[0285] Table 1 shows the amount of warping (mm) of the molded articlesproduced in Examples 1 to 14 and Comparative Example 1, together withthe quantities (g) of the material used for molding. TABLE 1 WarpingUsed quantity of Molding method (mm) material (g) Example 1 Hot runner0.7 200 Example 2 Hot runner 0.5 150 Example 3 Hot runner 0.5 150Example 4 Hot runner 0.4 150 Example 5 Hot runner 0.3 150 Example 6 Hotrunner 0.5 150 Example 7 Hot runner 0.5 150 Example 8 Hot runner 0.4 150Example 9 Hot runner 0.7 200 Example 10 Hot runner 0.3 150 Example 11Hot runner 0.3 150 Example 12 Hot runner 0.3 150 Example 13 Hot runner0.3 150 Example 14 Hot runner 0.3 150 Comparative Cold runner 1.5 450Example 1

[0286] It is clear from Table 1 that the amounts (weights) of thematerial used for producing molded articles were extremely small incomparison with that of the conventional molding using cold-runnersprues shown in Comparative Example 1, since each of the moldings inExamples 1 to 14 was hot-runner injection molding using hot-runnersprues.

[0287] In Examples 1 and 9, four gates (hot-runner sprues) were arrangedoutside the molded article, and the flow of the resin was ratherimbalanced. So, the molded articles obtained were rather greatly warped.On the contrary, in the other examples, since all the gates (hot-runnersprues) were located within the projected face of the molded article,the molded articles obtained were further less warped. Among them, inExamples 5 and 10, since all the gates (hot-runner sprues) were locatedwithin the projected face of the molded article and vertically andhorizontally symmetrical, the obtained molded articles were stillfurther less warped.

[0288] In Comparative Example 1, the weight of sprues thrown away aftercompletion of molding was as large as 300 g. In Examples 1 and 9, theweight of sprues thrown away was 50 g. In the respective examples andComparative Example 1, the weight of every molded article was 150 g.

[0289] In Comparative Example 1, since the gates of the respectivesprues could not be controlled because of cold-runner injection molding,the flow of the resin was likely to be imbalanced during molding, andthe obtained molded articles were very greatly warped.

INDUSTRIAL APPLICABILITY

[0290] According to the FRP molded article of the invention and theproduction process thereof, the quantity of sprue runners, a factor forraising the cost of the product, can be greatly decreased, and a producthaving good appearance can be obtained. Furthermore, the productobtained is less warped on a predetermined face.

1. An FRP molded article comprising a thermoplastic resin andresin-reinforcing fibers having an average fiber length of 0.1 to 7 mmdispersed in said thermoplastic resin, produced by a hot-runnerinjection molding.
 2. An FRP molded article according to claim 1,wherein said fibers are at least one kind of fibers selected from agroup consisting of carbon fibers, glass fibers and aramid fibers.
 3. AnFRP molded article according to claim 2, wherein the length of ahot-runner sprue used in said hot-runner injection molding is 10 to 600mm.
 4. An FRP molded article according to claim 3, wherein a depressionformed by the tip of a gate pin used for opening and closing a gateprovided at the tip of said hot-runner sprue exists on the surface ofthe molded article.
 5. An FRP molded article according to claim 4,wherein said depression has a diameter of 0.1 to 10 mm and a depth of 2mm or less.
 6. An FRP molded article according to any one of claims 1through 5, wherein said hot-runner injection molding has pluralhot-runner sprues having opening-closing gates at the tips thereofrespectively and each of said opening-closing gates is controlledindependently each other.
 7. An FRP molded article according to claim 6,wherein said hot-runner sprue comprises plural hot-runner sprues and aresin passing through a first sprue of an injection molding machinecommunicating to said plural hot-runner sprues passes through respectiveresin passages and is injected from the respective gates provided at thetips of the respective hot-runner sprues substantially at the sametiming.
 8. An FRP molded article according to claim 7, wherein thegeometrical lengths of said respective resin passages are equal to eachother.
 9. An FRP molded article according to claim 7, wherein there aretime differences in the opening and closing timings of said respectivegates.
 10. An FRP molded article according to any one of claims 1through 5 and 7 through 9, wherein said molded article is an equipmentbody.
 11. A molded article according to claim 6, wherein said moldedarticle is an equipment body.
 12. A process for producing an FRP moldedarticle, comprising: (a) a first step, in which resin pellets havingresin-reinforcing fibers having an average fiber length of 0.1 to 7 mmmixed in a thermoplastic resin used as a matrix resin are heated andmolten at 220 to 350° C. in a resin-melting cylinder of an injectionmolding machine, to prepare a molten resin having said fibers dispersedtherein, and (b) a second step, in which said molten resin obtained insaid first step is fed to a hot-runner sprue through a first sprue ofsaid injection molding machine and further through the resin passage ofa hot-runner injection molding apparatus; the gate of the hot-runnersprue is opened and closed to control the start and end of injection ofsaid molten resin into a cavity of a mold used for molding an article;said molten resin fed into said cavity is solidified in said mold; saidmold is opened; and the molded article is taken out.
 13. A process forproducing an FRP molded article according to claim 12, wherein thelength of said hot-runner sprue is 10 to 600 mm.
 14. A process forproducing an FRP molded article according to claim 13, wherein said gateis opened and closed by a gate pin going into and out of said gate, anda depression is formed on the surface of said molded article by the tipof said gate pin.
 15. A process for producing an FRP molded articleaccording to claim 14, wherein said depression has a diameter of 0.1 to10 mm and a depth of 2 mm or less.
 16. A process for producing an FRPmolded article according to any one of claims 12 through 15, whereinsaid hot-runner sprue comprises plural hot-runner sprues and the openingand closing of the respective gates provided at the tips of said pluralhot-runner sprues can be controlled respectively independently.
 17. Aprocess for producing an FRP molded article according to claim 16,wherein said hot-runner sprue comprises plural hot-runner sprues, andthe resin passing through a first sprue of an injection molding machinecommunicating to said plural hot-runner sprues passes through respectiveresin passages and is injected from the respective gates provided at thetips of the respective hot-runner sprues substantially at the sametiming.
 18. A process for producing an FRP molded article according toclaim 17, wherein the geometrical lengths of said respective resinpassages are equal to each other.
 19. A process for producing an FRPmolded article according to claim 17, wherein there are time differencesin the opening and closing timings of said respective gates.